1. Field of the Invention
The claimed invention relates to plasma display panels (PDPs) generally. More specifically, the invention relates to a method of driving a PDP and to a device for reducing the power consumption of a PDP and improving its contrast.
2. Description of the Related Art
A PDP is a display device that utilizes a plasma phenomenon to create and display color images. Each PDP includes millions of discharge cells. Each discharge cell is defined by barrier ribs formed between an upper substrate and a lower substrate. A dielectric layer is formed on each of the upper substrate and the lower substrate, and crossed electrodes intersect each discharge cell.
The interior of each discharge cell contains a gas in a vacuum state and is lined with a substance that emits visible colors of light when stimulated by ultraviolet radiation. Sustain electrodes (or X electrodes) and scan electrodes (or Y electrodes) are mounted on the upper substrate, and address electrodes are mounted on the lower substrate. In use, a voltage difference applied to the intersecting electrodes excites the gas atoms to release photons which impinge a colored phosphor that lines the interior of the discharge cell. The phosphor absorbs the incident photon and emits visible colored light. By selectively activating various combinations of electrodes, color images may be created.
In the conventional PDP described above, a drive voltage is supplied to the address electrodes and the scan electrodes to thereby affect an address discharge between the same. Wall charges are formed on the dielectric layers of the upper substrate and the lower substrate as a result. Also, in the cells selected by the address discharge, an alternating signal applied to the scan electrodes and the sustain electrodes creates a sustain discharge.
FIG. 1 shows a perspective view of a conventional AC PDP.
As described above, the PDP includes a scan electrode 4 and a sustain electrode 5. Disposed over a dielectric layer 2 and a protection film 3, the electrodes 4 and 5 are provided in parallel and form pairs with each other under a first glass substrate 1. A plurality of address electrodes 8 covered with an insulation layer 7 are installed on a second glass substrate 6. Barrier ribs 9 are formed in parallel with the address electrodes 8, on the insulation layer 7 between the address electrodes 8. Additionally, a phosphor 10 is formed on the surface of the insulation layer 7 between the barrier ribs 9. The first and second glass substrates 1 and 6, having a discharge space 11 between them, are provided facing each other so that the scan electrode 4 and the sustain electrode 5 may respectively cross the address electrode 8. The address electrode 8 and a discharge space 11 formed at an intersection of the scan electrode 4 and the sustain electrode 5 form a discharge cell 12.
FIG. 2 is a diagram illustrating the arrangement of electrodes in a conventional PDP. The discharge cell 12 shown in FIG. 2 corresponds to the discharge cell 12 shown in FIG. 1.
As shown, a conventional PDP electrode has an m×n matrix configuration, in which address electrodes A1 to Am are arranged in the column direction. Scan electrodes Y1 to Yn and sustain electrodes X1 to Xn are alternately arranged in the row direction. The scan electrodes will be noted as “Y electrodes” and the sustain electrodes as “X electrodes.”
FIG. 3 is a diagram illustrating a driving waveform used in a conventional PDP. As the diagram illustrates, the conventional PDP driving method requires that each subfield have a reset interval, an address interval, and a sustain interval.
In the reset interval, wall charges that were formed by a previous sustain discharge are erased, and the states of the cells are reset in order to fluently perform a next address operation. A conventional reset interval includes an erase interval, a Y ramp rising interval, and a Y ramp falling interval.
In the erase interval, an erase ramp voltage that gradually rises from 0V to +Ve(V) is applied to the X electrode. This erases the wall charges between the X electrode and the Y electrode.
In the Y ramp rising interval, the address electrode and the X electrode are maintained at 0V, and a ramp voltage that gradually rises from a voltage of V1 to a voltage of V2 is applied to the Y electrode. V2 is greater than a discharge firing voltage with respect to the X electrode at 0V, and V1 is less than the discharge firing voltage with respect to the X electrode at 0V. While the ramp voltage rises, a first weak reset discharge occurs in all the discharge cells from the Y electrode to the address electrode and the X electrode.
In the Y ramp falling interval, a ramp voltage that gradually falls from a voltage of V1 to a voltage of V3 is applied to the Y electrode while the X electrode is maintained at a constant voltage of Ve. V3 is greater than a discharge firing voltage with respect to the X electrode at Ve, and V1 is less than the discharge firing voltage with respect to the X electrode at Ve. While this ramp voltage is falling, a second weak reset discharge occurs in all the discharge cells.
When the reset operations are finished, scan pulses are sequentially applied to the Y electrode, and the wall charges are accumulated on the cells to which address data is applied.
The sustain interval is a period for performing a discharge that displays images on the addressed cells. When the sustain interval starts, sustain pulses are alternately applied to the X and Y electrodes, a sustain discharge is performed, and images are displayed.
The conventional PDP driving method noted above performs the reset operation and the address operation irrespective of whether address data is provided in each subfield. Significant disadvantages associated with this approach are increased background brightness, degraded contrast, and increased power consumption. For example, a high-resolution PDP needs a plurality of scan electrodes and subfields. Consequently a PDP with a large display area increases the line capacitance for each line and also increases a scan bias voltage; both of which increase power consumption. The increase of power consumption causes other problems such as raising the temperature of a scan IC (integrated circuit) above normal operating limits. This also degrades picture quality.
A solution is needed that provides a PDP having decreased background brightness, decreased power consumption, and improved contrast.